C: Food Chemistry Precipitation of Salivary Proteins After the Interaction with Wine: The Effect of Ethanol, pH, Fructose, and Mannoproteins Alessandra Rinaldi, Angelita Gambuti, and Luigi Moio Abstract: Astringency is a complex sensation mainly caused by the precipitation of salivary proteins with polyphenols. In wine it can be enhanced or reduced depending on the composition of the medium. In order to investigate the effect of ethanol, tartaric acid, fructose, and commercial mannoproteins (MPs) addition on the precipitation of salivary proteins, the saliva precipitation index (SPI) was determined by means of the sodium dodecyl sulphate polyacrylamide gel electrophoresis of human saliva after the reaction with Merlot wines and model solutions. Gelatin index, ethanol index, and Folin–Ciocalteu index were also determined. As resulted by Pearson’s correlation, data on SPI were well correlated with the sensory analysis performed on the same samples. In a second experiment, increasing the ethanol (11%–13%–17%), MPs (0–2–8 g/L), fructose (0–2–6 g/L) level, and pH values (2.9–3.0–3.6), a decrease in the precipitation of salivary proteins was observed. A difference in the SPI between model solution and red wine stated that an influence of wine matrix on the precipitation of salivary proteins occurred. Keywords: astringency, ethanol, fructose, mannoproteins, salivary proteins precipitation, tartaric acid Practical Application: Results provide interesting suggestions for enologists, which could modulate the astringency of red wine by: (i) leaving some residual reducing sugars (such as fructose) in red wine during winemaking of grapes rich in tannins; (ii) avoiding the lowering of pH; (iii) adding commercial mannoproteins or promoting a “sur lie” aging; and (iv) harvesting grapes at high technological maturity in order to obtain wines with a satisfactory alcoholic content when possible. Introduction Astringency may be considered the resulting of different sensa- tions as drying, roughing, and puckering of the epithelium (Lee and Lawless 1991) felt in the mouth after the ingestion of foods and beverages containing polyphenols. This mouthfeel is localized not only in specific regions of the tongue, as it happens for the gus- tative sensations, but it also involves the overall buccal cavity like soft palate, gingives, and lips (Breslin and others1993). One of the main mechanisms that have been proposed to explain astringency is based on the chemical interactions of some salivary constituents with polyphenols and on the formation of protein–polyphenol complexes. The precipitation of these complexes is able to stim- ulate mechanoreceptors connected with trigeminal nerve and to transmit to brain the perception of astringency. This results in tactile sensations characterized by different astringent subqualities, as described by the mouthfeel wheel (Gawel and others 2000). Other scientists considered astringency a taste because like sour, sweet, salty, and bitter compounds, astringent stimulus is able to MS 20111424 Submitted 11/25/2011, Accepted 1/12/2012. Author Rinaldi is with Dipt. di Scienze degli Alimenti, Univ. di Napoli Federico II, Facolt` a di Agraria, Via Universit` a 100, 80055, Portici (Na), Italy; and Laffort, BP 17, 33015 Bordeaux Cedex, France. Authors Gambuti and Moio are with Dipt. di Scienze degli Alimenti, Univ. di Napoli Federico II, Facolt` a di Agraria, Via Univ. 100, 80055, Portici (Na), Italy. Direct inquiries to author Rinaldi (E-mail: alessandra.rinaldi@unina.it). activate signal transduction pathways (Spielman 1990). However, the weight of evidence favors the tactile sensation as principally caused when astringent substances precipitate salivary proteins that give saliva its lubricity (Breslin and others 1993). During last decades, astringency has been largely studied in red wine, because it represents an important quality attribute. Wine is a complex matrix and its taste perception is determined by a bal- ance among sensory active compounds like acids, sugars, ethanol, and others. All these gustatory stimuli have been shown to affect the perception of astringency. Adding acids to wines or tannic acid solutions produced an increase in astringency (Guinard and others 1986). On the contrary, the addition of sweeteners was observed to attenuate the mouth dryness typical of the astringent sensation both of tannic acid solutions (Lyman and Green 1990) and red wine (Ishikawa and Noble 1995). The astringent sensation can also be altered by the presence of the most important component of wine: the ethanol (Lesschaeve and Noble 2005). As the ethanol level increased in model solution (Fontoin and others 2008), a de- crease in perceived astringency and in some astringent subqualities (Vidal and others 2004a) was observed. In case of red wine, astrin- gency sensation was affected by alcohol reduction (Meillon and others 2009). Astringency can also be modulated by the presence of some polysaccharides, such as mannoproteins (MPs), decreasing the intensity of some astringent attributes and contributing to the fullness of model wine solutions (Vidal and others 2004b). During tasting, the influence of wine components on astrin- gency perception may involve different mechanisms that govern C  2012 Institute of Food Technologists R  doi: 10.1111/j.1750-3841.2012.02639.x Vol. 77, Nr. 4, 2012  Journal of Food Science C485 Further reproduction without permission is prohibited